Effects of voluntary exercise on heart function in streptozotocin (STZ) – induced diabetic rat

Abstract

Exercise training improves cardiac performance and has been utilized as an effective adjunct to pharmacotherapy in themanagement of diabetes mellitus. The aims of this study were to characterize voluntary exercise habits in streptozotocin(STZ)-induced diabetic rats and investigate whether attained levels of voluntary exercise induce effects on diabetic heartfunction. Diabetes was induced by a single intraperitoneal injection of STZ (60 mg/kg). Animals were divided into 4 groups:Control Sedentary (CS), Diabetic Sedentary (DS), Control Running (CR) and Diabetic Running (DR). DR and CR rats wereprovided with running wheels. Body weight and blood glucose were measured in running rats at the start and end of the 60-day exercise period. Ventricular action potentials were measured in spontaneously beating heart. Shortening and intracellularCa2+ were measured in electrically stimulated ventricular myocytes. DR rats exercised less than CR rats. At 60 days the meandistance covered by DR rats was 1027 ± 289 m compared to 5975 ± 1117 m in CR rats. CR gained whilst DR rats lost weightat the end of the exercise period. Mean blood glucose in CR and DR rats at the start of the exercise period was 71 ± 4 and 426± 21 mg/dl, respectively. Glucose levels were not altered in CR rats but were reduced in DR rats at the end of the exerciseperiod. The time to peak shortening and peak Ca2+ transient and time to half relaxation of the Ca2+ transient were prolongedin myocytes from DS compared to CS rats and were not additionally altered by voluntary exercise. In conclusion, diabeticrats were less inclined to partake in voluntary exercise compared to controls and the levels and duration of exercise wereinsufficient to significantly alter cardiac performance in either control or diabetic rats. (Int J Diabetes Metab 15: 32-37,2007)